Т е к с т 8. New Air Guidance Systems

(3.200)

Introduction

Under the steady increasing air traffic in most principal airports of the big cities around the world as well as the more strict environmental regulations imposed to airports, the air traffic controllers and pilots encounter with heavier challenges during approach and landing. Many efforts have been devoted to develop new guidance control methods to cope with these problems such as traffic avoidance and relative guidance maneuvers, formation flight, continuous descent approaches, time metering and landing maneuvers. It has become more and more difficult to integrate these new complex functions within the classical discrete mode-based approach of guidance where complex trajectories are performed through the scheduling of elementary guidance.

Until recently few works have been published by the flight control community to deal with what seems more profitable and safe in that case: a full trajectory-based approach of flight guidance. Similar needs appear today, when considering activities, performed by other autonomous vehicles, such as helicopters, space and sea ships and other surface or under water vehicles.

The approach, proposed in this communication to design efficient guidance systems is based on the following considerations:

– In general the guidance dynamics related with the trajectory followed by a vehicle are quite slower than its rotational dynamics. The latter are often already controlled by basic autopilots and stabilizers coping with the natural fast dynamical modes and the actuators nonlinearities.

– It appears, that in many situations, the guidance dynamics relating the attitude parameters of the vehicle to the coordinates of its center of gravity are differentially flat, so that this property can be used to generate from a planned trajectory, attitude reference values to be submitted to an autopilot in charge of the rotational dynamics.

– In many cases, the guidance dynamics flatness property is implicit, so that their analytical inversion is not feasible and a numerical device, designed to perform an on-line inversion, should be developed.

– The direct application of the resulting nominal reference values to a basic autopilot should result in an open loop control approach with poor tracking accuracy and increasing trajectory drift.

– Today, navigation systems present improved performances and their output can be used in control schemes providing on-line tracking corrections directives, so that the open loop structure can be completed by a flight guidance closed loop control scheme.

The performances of the resulting guidance system are strongly dependent on the dynamic accuracy of the navigation system and this at two levels:

– data, collected for neutral network training purpose is corrupted by navigation errors and this generates systematic errors for the reference flight parameter values, submitted to the autopilot,

– the on-line compensation relies directly on position, speed and acceleration estimates obtained from the navigation systems. Particularly in the case of aircraft, estimates of the wind speed and wind acceleration components must be available to take into account the wind effect on the actual trajectory.